The present invention relates generally to monitoring the channel power levels of communication signals. More specifically, the invention relates to the monitoring of optical signals in optical fiber telecommunication systems and networks, particularly to the case in which the monitoring is accomplished with a channel power monitor based on a variable optical channel attenuator.
In modern fiber optic telecommunication systems and networks, the signals are transmitted along optical fibers. Each optical fiber can carry an independent signal in each of multiple signal channels. The signal in an optical fiber typically requires periodic amplification to maintain appropriate signal strength. To properly amplify the signal, smart amplifiers routinely require information regarding the channel power level in each of the channels transmitted by the fiber. In optical systems, each channel is characterized by a wavelength that is representative of the wavelengths in the channel. A diffraction-grating spectrum analyzer or a Fabry-Perot spectrometer could be used to determine the channel power levels, but these devices tend to be costly. What is desired is a channel power monitor that can easily be made low-cost, small and compact.
The current invention provides an apparatus and method for the monitoring channel power levels in a number of signal channels. Although the invention was motivated by the need to monitor the channel power levels in optical fiber systems, the invention is not restricted to the optical range of the electromagnetic spectrum, or even to electromagnetic signals, but can be applied generally to any system with multiple channels that require monitoring.
Various embodiments of the invention involve methods for monitoring channel power levels of input signals. Each of N signal channels is characterized by a channel parameter xcexi, where i is an index in the range 1xe2x89xa6ixe2x89xa6N. The value of each channel power level is designated as p(xcexi).
In one embodiment a set of M attenuation profiles is provided, where Mxe2x89xa7N. Each attenuation profile is characterized as a function of the channel parameter xcexi by a k-th attenuation profile Ak(xcexi), and k is a profile index. The profile index k is initialized to a value of 1. An input signal is attenuated according the k-th attenuation profile Ak(xcexi), thereby producing an attenuated power level in each signal channel. A k-th integrated attenuated power level is measured. The k-th integrated attenuated power level is the attenuated power level integrated over the N signal channels after application of the k-th attenuation profile. The value of the k-th integrated attenuated power level is represented by Pk. The index k is then incremented by 1 and the attenuating, measuring, and incrementing steps are then repeated until k greater than M. M values of Pk are then available. Because the Mxe2x89xa7N and all the Ak(xcexi) are known, the following set of linear equations are solved for p(xcexi):       P    k    =            ∑              i        =        1            N        ⁢          xe2x80x83        ⁢                            A          k                ⁡                  (                      λ            i                    )                    ⁢              p        ⁡                  (                      λ            i                    )                    
for 1xe2x89xa6kxe2x89xa6M.
In another embodiment the input signal is split into M substantially identical scaled input signals represented by r(xcexi), where r(xcexi)=xcex1(xcexi) p(xcexi) and xcex1(xcexi) is a known scaling function. Each scaled input signal is attenuated according to a different attenuation profile Ak(xcexi), thereby producing M attenuated power levels for each signal channel. M integrated attenuated power levels are measured, the value of the k-th integrated attenuated power level being represented by Pk. The following set of linear equations are solved for r(xcexi)       P    k    =            ∑              i        =        1            N        ⁢          xe2x80x83        ⁢                            A          k                ⁡                  (                      λ            i                    )                    ⁢              r        ⁡                  (                      λ            i                    )                    
for 1xe2x89xa6kxe2x89xa6M. The channel power level p(xcexi) is determined from p(xcexi)=r(xcexi)/xcex1(xcexi).
An apparatus for monitoring channel power levels includes a variable channel attenuator that has multiple attenuation profiles. The apparatus further includes a detector for measuring integrated attenuated power levels, and an analysis unit that receives all of the values of the integrated attenuated power levels. The analysis unit solves a set of linear equations to obtain the values of the channel power levels.
An alternative apparatus includes a splitter for splitting the input signal into M scaled input signals. The scaled input signals are then attenuated by any appropriate means, whether that be a variable channel attenuator, multiple individual attenuators, or some other means. Multiple detectors are preferably used to measure the integrated attenuated power levels. The analysis unit solves modified equations to determine the values of the channel power levels.
Additional features and advantages of the invention will be set forth in part in the description that follows, and in part will be obvious from the description, or may be learned by practice of the invention. Various embodiments of the invention do not necessarily include all of the stated features or achieve all of the stated advantages.